This Phase I grant titled, "Simultaneous SPECT/CT with a single photon counting camera" will enable the development of a fast photon-counting x-ray and gamma-ray imaging array with energy discrimination. The aims of the project when completed will demonstrate several advances in the technologies used to fabricate vertically integrated dense arrays. Recently, new technological developments in connecting sensors to the reduced size of application specific integrated circuits (ASICs) has been applied to reading out semiconductor detectors These advances, along with improvements to the cost and reliability of the compound semiconductor cadmium telluride (CdTe), allow us to develop a photon counting detector and read-out technology for higher spatial resolution single photon emission computed tomography (SPECT) and energy resolved single photon counting x-ray computed tomography (CT) at reduced dose. These detectors improve spatial resolution in SPECT imaging with direct conversion CdTe sensors and 0.5 mm pixels which are three times smaller than currently available commercially. These same detectors, which maintain good energy resolution up to 5 W 106 counts per second per pixel (the world's fastest output count rate), enable significant improvements in CT imaging such as reduced patient dose while maintaining excellent image quality, enhanced tissue contrast, and material decomposition capabilities (tissue type identification). Photon counting detectors with energy binning can improve CT performance by counting and binning each x-ray detected. Additionally, the simultaneous acquisition of anatomical and functional data from identical image volumes will reduce coregistration errors which will be extremely important for the accurate anatomical localization of uptake on sub- millimeter length scales. This project produces several important technological innovations. These include the fabrication of single crystal CdTe detectors with an active area extending to the edge of the crystals (no guard rings) which allows tiling with almost no dead space. Additionally, we have developed packaging and encapsulation methods to connect dense multi channel fast application specific integrated circuits (ASICs) to the crystals and formed within the active area of the crystal to preserve tiling in two dimensions. And we achieve a rapid signal formation, shorter than the transit time for charge carriers across the CdTe crystal. In this Phase I project we will demonstrate a vertically integrated photon counting SPECT and CT detector with energy binning and read-out that is capable of producing higher spatial resolution SPECT and energy resolved CT which can deliver less radiation dose and differentiate between tissue types. Achieving vertical integration while maintaining performance will allow the tiling of Phase I modules in Phase II to larger fields of view. The innovative methods described in this proposal could have a tremendous significance by developing methods that improve SPECT and CT imaging and could one day be translated to the clinic. There remains however a large risk in the final integration of the vertical readout ASICs to the CdTe detectors. As we are developing the world's fastest x-ray and gamma-ray detector arrays by using the latest and smallest bonding techniques available, this is not a low risk step in the development. Completion of the Phase I milestones in a vertically integrated array will successfully address this risk as well as demonstrate significantly improved performance as compared to the currently available SPECT and CT detectors. PUBLIC HEALTH RELEVANCE: We are developing fast photon counting arrays for x-ray and gamma-ray imaging. This new detector technology can potentially reduce dose and improve contrast when applied to x-ray CT. Additionally, the detector can perform simultaneous SPECT and CT. The proposal submitted contains several innovative advancements to the current state of the art technologies employed in both CT and SPECT.